全文获取类型
收费全文 | 569575篇 |
免费 | 5028篇 |
国内免费 | 1690篇 |
专业分类
化学 | 292538篇 |
晶体学 | 8252篇 |
力学 | 25908篇 |
综合类 | 12篇 |
数学 | 78389篇 |
物理学 | 171194篇 |
出版年
2020年 | 3762篇 |
2019年 | 4040篇 |
2018年 | 12063篇 |
2017年 | 12689篇 |
2016年 | 11059篇 |
2015年 | 5999篇 |
2014年 | 7905篇 |
2013年 | 21955篇 |
2012年 | 19924篇 |
2011年 | 30199篇 |
2010年 | 19343篇 |
2009年 | 19222篇 |
2008年 | 27385篇 |
2007年 | 30404篇 |
2006年 | 18394篇 |
2005年 | 22201篇 |
2004年 | 17708篇 |
2003年 | 16178篇 |
2002年 | 14293篇 |
2001年 | 14567篇 |
2000年 | 11464篇 |
1999年 | 8768篇 |
1998年 | 7305篇 |
1997年 | 7175篇 |
1996年 | 7147篇 |
1995年 | 6301篇 |
1994年 | 6111篇 |
1993年 | 5945篇 |
1992年 | 6476篇 |
1991年 | 6440篇 |
1990年 | 6108篇 |
1989年 | 5880篇 |
1988年 | 6115篇 |
1987年 | 5805篇 |
1986年 | 5533篇 |
1985年 | 7755篇 |
1984年 | 7964篇 |
1983年 | 6489篇 |
1982年 | 7063篇 |
1981年 | 7003篇 |
1980年 | 6614篇 |
1979年 | 6907篇 |
1978年 | 7051篇 |
1977年 | 6969篇 |
1976年 | 6940篇 |
1975年 | 6669篇 |
1974年 | 6544篇 |
1973年 | 6855篇 |
1972年 | 4173篇 |
1971年 | 3381篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
We describe a new algorithm which uses the trajectories of a discrete dynamical system to sample the domain of an unconstrained objective function in search of global minima. The algorithm is unusually adept at avoiding nonoptimal local minima and successfully converging to a global minimum. Trajectories generated by the algorithm for objective functions with many local minima exhibit chaotic behavior, in the sense that they are extremely sensitive to changes in initial conditions and system parameters. In this context, chaos seems to have a beneficial effect: failure to converge to a global minimum from a given initial point can often be rectified by making arbitrarily small changes in the system parameters. 相似文献
102.
103.
Possibilities for the control of the parameters of free-polarization decay (FPD), optical nutation, and photon echo (PE) using the dressing field are studied. Coherent transients are generated with the Stark switching technique and are detected in the radiation of the probe field polarized orthogonally to the dressing field. The evolution-operator technique is employed in the calculations. The experiments are performed at the R(4, 3) transition of the 0 ? 1 v3 13CH3F vibrational band with the radiation of a cw CO2 laser. It is theoretically and experimentally demonstrated that FPD and PE are suppressed upon an increase in the intensity of the dressing field. The observed shapes of the transient FPD and PE signals and their variations with the dressing field intensity are in qualitative agreement with the results of the calculations. 相似文献
104.
A practical Sonogashira alkynylation protocol for the preparation of 8-alkynylated adenosines and guanosines has been developed. Protection of the sugar hydroxyl substituents is not required; protection hinders the purification of these products. A preliminary fluorescent study is reported, which shows that the presence of a substituent on the phenylene ring influences the fluorescent properties considerably, an outcome that could be utilized in biological applications. 相似文献
105.
N. S. Simonović 《Few-Body Systems》2006,38(2-4):139-145
In agreement with the Kohn theorem the relative motion (rel) of three electrons in a two-dimensional parabolic trap separates
from the centre-of-mass (CM) motion. By introducing new coordinates the Hamiltonian for relative motion in the approximation
of non-interacting electrons can be taken to the normal form. The eigenstates of the normalized Hamiltonian are products of
the Fock-Darwin states for normal modes. The energy levels for relative motion are obtained by diagonalizing the exact Hamiltonian
in the eigenbasis for the non-interacting case. In this basis the interaction matrix elements can be obtained in the analytical
form. Since the rank of the Hamiltonian matrix is significantly reduced, the calculations are faster and more accurate than
those for the full (CM + rel) motion. This advantage is especially important for the calculations of excited states and the
analysis of energy spectra. 相似文献
106.
On Quantum Team Games 总被引:2,自引:0,他引:2
E. Ahmed M. F. Elettreby A. S. Hegazi 《International Journal of Theoretical Physics》2006,45(5):880-886
Recently Liu and Simaan (2004) convex static multi-team classical games have been introduced. Here they are generalized to both nonconvex, dynamic and quantum games. Puu's incomplete information dynamical systems are modified and applied to Cournot team game. The replicator dynamics of the quantum prisoner's dilemma game is also studied. 相似文献
107.
We present the design and study of waveguide structures based on porous silicon where the light confinement is not due to the usual total reflection effect but to the use of photonic crystals (PCs) as confining walls. These PC are omnidirectional mirrors (OMs), consisting of the periodic repetition of two porous silicon layers with different refractive indices and thicknesses. They reflect the radiation for all angles of incidence within a frequency range called the omnidirectional band gap (OBG). We have followed the PC formalism to investigate the properties of the OM as a multimode waveguide: the number of modes within the band gap, their field spatial distribution and their confinement as a function of the frequency and the core thickness. 相似文献
108.
Analytical expressions are obtained that describe the changes in the degree of coherence and in the thickness of the coherence layers occurring upon propagation of a dispersed broadband laser beam. It is found that the greater the tilting of the coherence layers with respect to the phase fronts, the more rapidly the spatial coherence is violated with increasing distance. A comparison with the case of an undispersed beam is performed. It is shown that, as the beam propagates, the decrease in the degree of coherence is accompanied by the appearance of spatial fluctuations of this parameter. The degree of mutual coherence of intersecting dispersed beams with parallel correlated coherence layers, which determines the efficiency of their coherent interaction, is investigated. The existence of spatial fluctuations of the degree of mutual coherence is established. 相似文献
109.
A. V. Semykin I. A. Kazarinov E. A. Khomskaya 《Russian Journal of Electrochemistry》2006,42(6):643-648
The hydrogen ionization process is studied experimentally on an industrial sintered nickel oxide electrode in models of sealed nickel-metal hydride batteries. It is shown that the hydrogen ionization rates that are reached during overcharge by high current densities in conditions of forced gas delivery into the electrode pores (up to 40 mA cm?2) exceed the self-discharge rate of a nickel-hydrogen battery by two orders of magnitude. Up to 70% of hydrogen delivered into the compact assembly block undergoes ionization during forced charge of models of sealed nickel-metal hydride batteries with a closed hydrogen cycle. Two independent methods (potentiostatic and manometric) are used to determine the relationship between rates of hydrogen ionization with the degree of the electrode filling with gas and perform estimation of the process intensity at a unit reaction surface. It is established that, in conditions of forced gas delivery, practically all the hydrogen oxidation current is generated at the surface of the nickel oxide electrode beneath thin films of an electrolyte solution at the rate of 4–5 mA cm?2. It is shown that the hydrogen oxidation rate on a nickel oxide electrode filled in part by gas is independent of the electrode potential, probably because of a tangible contribution made by diffusion limitations to the overall hampering of the process. 相似文献
110.
V. Edon M.C. Hugon B. Agius L. Miotti C. Radtke F. Tatsch J.J. Ganem I. Trimaille I.J.R. Baumvol 《Applied Physics A: Materials Science & Processing》2006,83(2):289-293
The influence of processing parameters on the electrical characteristics of RuO2/LaAlO3/Si metal-oxide-semiconductor structures was investigated. In particular, the sputtering regime during deposition of LaAlO3 on Si and the atmosphere used in the post-deposition annealing step were addressed by determining capacitance-voltage and
gate current-voltage characteristics. These results were correlated with compositional information obtained by Rutherford
backscattering spectrometry and nuclear reaction analysis. A post-deposition annealing step in oxygen at 600 °C resulted in
better electrical characteristics of the final structure as compared to the same treatment performed in nitrogen. This result
is explained by oxygen ability to heal oxygen vacancies in the LaAlO3 film, especially at the dielectric/semiconductor interface region. A thermalized sputtering regime during deposition of LaAlO3 on Si leads to capacitors with electrical characteristics superior to those deposited in ballistic regime.
PACS 77.84.Dy; 81.15.Cd; 81.40.Gh; 73.40.Qv; 82.80.Yc 相似文献